Current industrial automotive trends to reduce the number of overall mechanical components of the vehicle and to reduce the overall vehicle weight have contributed to the development of system-by-wire applications, typically referred to as X-by-wire systems. Once such X-by-wire system that has recently received increased attention is a brake-by-wire (BBW) system, sometimes referred to as an electronic braking system (EBS).
Unlike conventional mechanical braking systems, BBW systems actuate one or more vehicle braking components via an electric signal generated by an on-board processor/controller or received from a source external to the vehicle. In some systems, a BBW system is effected by supplanting a conventional hydraulic fluid-based service braking system with an electrical base system to perform basic braking functions. Such a system is typically provided with a manually actuated back-up system that may be hydraulically operated.
Since BBW systems typically remove any direct mechanical linkages and/or or hydraulic force-transmitting-paths between the vehicle operator and the brake control units, much attention has been given to designing BBW control systems and control architectures that ensure reliable and robust operation. Various design techniques have been implemented to promote the reliability of BBW systems including, for example, redundancy, fault tolerance to undesired events (e.g., events affecting control signals, data, hardware, software or other elements of such systems), fault monitoring and recovery. One design approach to provide fault tolerance which has been utilized in BBW brake control systems has been to include a mechanical backup system that may be utilized as an alternate means for braking the vehicle.